I was planning on using crushed oyster shell powder for my next organic grow. I didn't realize that oyster shell powder means ancient deposits of oyster shells that are mined and then turn into a powder, I thought it just means regular oyster shells crushed to a powder. Now I have 10kg of homemade oyster shell powder from regular oyster shells but apparently, they take so long to break down that it's not really useful. Does anyone have any input on this or even better, experience with it? I can't buy the proper oyster shell powder because it's not available in my country and too expensive to import.